How Pre-Dive Switches Work | #scuba #regulator | @ScubaDiverMagazine

How Pre-Dive Switches Work | #scuba #regulator | @ScubaDiverMagazine
Pre-Dive Switches or Venturi Levers help to prevent a freeflowing regulator by disrupting airflow inside a 2nd stage.
#scuba #scubadiving #scubadiver
LINKS

Join this channel to get access to perks:

SUPPORT THE CHANNEL
You can help support the channel in three easy ways;

2. Use our affiliate link to make your next scuba purchases

3. Subscribe to one of our print or digital magazines

-----------------------------------------------------------------------------------
╔═╦╗╔╦╗╔═╦═╦╦╦╦╗╔═╗
║╚╣║║║╚╣╚╣╔╣╔╣║╚╣═╣
╠╗║╚╝║║╠╗║╚╣║║║║║═╣
╚═╩══╩═╩═╩═╩╝╚╩═╩═╝

-----------------------------------------------------------------------------------
-----------------------------------------------------------------------------------
Follow Us On Social Media
00:00 Introduction
00:36 Venturi Effect
02:01 Pre-Dive Switch
02:55 When to Use

[Bayok]

Constructive criticism: there was one area of content that was not clear. It was easy to follow the open vs covered in the switch, but didn’t go over the switch meaning of + vs -. And then you used terms of on vs off. It left me a little confused when you said on and off. Does on mean activated, thus restricting the air flow or does on mean full unrestricted air flow? My comment is that these terms should be fully explained/correlated to the general audience at the beginning just like explaining an acronym at first use. I love all your extremely helpful instructional videos and value every one of your posts. I do hope you take this comment as a very friendly one from one of your active followers.

[Dive-D]

Laughs in DACOR PACER: The Pacer's Venturamatic System is the best innovation ever made in a 2nd stage. No adjustability needed, is all automatic, and it will never free flow.

[leemiller]

Glad to see I'm not alone in having trouble remembering+/- and should I push the switch away or towards my mouth while diving. I have the same issue remembering which way to turn the adjustment knob, too. I end up going with what feels right at the time.

[bloodymarvelous]

I have the MTX and MTXV, and I opened both up.
The MTX doesn't have a Venturi switch, and the opening is always covered.
On the MTXV you can open the Venturi for additional gas flow.

I therefor have to conclude that a regulator without a Venturi switch exists not to prevent a freeflow, but to allow for the Venturi effect to force more gas into your lungs, which is useful if you're working harder underwater, like when swimming against a current.

Now, I haven't looked at cheaper regulators, but I would assume that regulators without Venturi switches have the opening covered to prevent freeflows, and thus aren't (as) susceptible to it.

[hughidiyit]

As a Mares Abyss diver, I had to smile.

[cecillee]

Thank you for your very clear and comprehensive explanation. I'm new to scuba diving (I just got certified as a PADI Open Water Diver and Advanced Open Water Diver at a resort on Ko Racha Yai 12NM south of Phuket, but am basically a newbie) and am keen to understand just what I'm supposed to do and why. I've been staring at the two levers/dials on my second stage and wondering what they are and why they're there. This video has answered both questions. Wishing you a blessed Christmas and safe and enjoyable dives in the years ahead.

[mikeyduke]

Been looking for a video about this.

On my second ever open water dive a few weeks ago (I'm in the UK the water was 5 degrees C) my instructor wanted to practice mask clearing in very shallow water (I'm not sure this helped but I was her idea) and I'm not sure if it was cold water shock or a problem with the regulator but as soon as I put my face underwater (in chest deep water) I couldn't breath in or out without my mask on even if I tried to push very hard.
Eventually she kind of had an idea and I breathed on her octopus and it worked but then she put the reg to positive and I breathed but it was still quite hard and only a few breathes.


Essentially now knowing more about the situation I had used the reg in shallow/out of water quite a lot (about 15mins of messing about trying and stopping to catch my breath and not get annoyed).
We came out of the water for a break and then went down to 2metres and started the lesson.
As I took my regulator out to show the skill the regulator freeflowed and we both just stared at it for a second before she passed me her octopus and we made a shared air ascent...
In fairness I made a few mistakes at the surface and didn't inflate my jacket as I was just watching what she was doing and my mind blanked so she shouted for assistance and they (the diving centre we were at) launched a boat to come and help me and turned off the cylinder which the 1st stage had frozen over by this point...

Straight away the staff from the diving centre (where the kit was hired) were onto her about why was my regulator on positive when they had given it to me on negative that morning...

Having learnt more about the situation I realised obviously the problem was the open air breathing in shallow water most likely....

But this video gives me more of an understanding of the equipment but less of an understanding of the situation and why the centre staff were so obsessed with it being in the positive position

[josephdracula]

#ask mark Hello Mark always enjoy your shows. My question is about wing bladders. What comes to mind is why a 18 pound lift and a 30 pound lift. If the 18 is more than sufficient why do some divers use a 30 pound. Is it because of gear or steel tanks. I have heard of just the convenience for traveling. I noticed most divers are in warm water conditions with no more than a 3 mil wetsuit. Maybe you can go into more detail. Thanks Joe

[Yggdrasil]

#askmark I'd love to know how a drysuit shoulder valve works. How does it dump air without letting in water? How does its adjustability work?